Such an electrostatic sensor system is typically provided on two objects that can assume different spatial configurations relative to one another and between which a body of a living thing can be place and by means of which one can detect whether this body is between the two objects.
A measuring arrangement for detecting the position of a motor-vehicle occupant is known from U.S. Pat. No. 6,439,333 that can detect the position of a motor-vehicle occupant in very maximally reliable and failsafe manner in order to enable the differentiated triggering of an airbag according to need. A distance measurement is performed with this known sensor and measuring system, with a seat belt of a seat-belt assembly that is in physical contact with the motor-vehicle occupant serving as an active reference position. The spacing between the seat belt of the seat-belt assembly and fixed and known points predefined within the interior of the vehicle enables the correct detection of the spatial position of the seat belt and, through that, of the motor-vehicle occupant. The spacing is measured by magnetic-field transceivers whose transmitters are advantageously in the strap of the seat-belt assembly.
One drawback of this known measuring and sensor system is that the body of a living thing whose spatial position is to be determined through detection of the seat belt hardly absorbs magnetic fields. As a result, while spacing measurements can be performed by means of the known measuring system, no distinction can be drawn using this measuring system regarding whether contact exists between the seat belt and the body of the living thing or between the seat belt and another object. Moreover, the application of magnetic fields to the thoracic region is associated with certain disadvantages and risks. The influencing or disruption of pacemakers that may be present cannot be ruled out; moreover, the magnetic strips of EC cards or cards of other types that are commonly carried in the breast pockets of articles of clothing worn by motor-vehicle occupants, for example, might be erased by the magnetic fields. What is more, a readily detectable magnetic field requires either a large number of windings or a high current. The introduction of windings or conductor loops into a fabric is associated with a relatively high level of technical effort.
A sensor system for detecting a change in the position of a motor-vehicle occupants is known from DE 10 2008 044 903 in which at least one electrode in a motor-vehicle seat for transmitting a signal and at least one other electrode for receiving the signal are provided. The position of the motor-vehicle occupant is determined through differential measurement of individual electrode signals relative to reference electrodes. In this known sensor system, the problem of fluctuating and substantially undefined coupling factors between a transmitting electrode and the body of a living thing and the undefined coupling factor between a receiving electrode and the body of a living thing is resolved. A sensor system is therefore provided with a plurality of receiving antennas, with the evaluation being performed by comparison of the induced signal voltages in the receiving antennas. One drawback of the measuring and sensor system known from DE 10 2008 044 903 is that the differences between the induced signals in the receiving antennas are evaluated. But these, in turn, are dependent on coupling factors.
A sensor and measuring system is known from EP 2 937 251 that is intended to make it possible to detect whether the seat belt of a seat-belt assembly is properly in place on a motor-vehicle seat. A sensor is provided spaced from the seat and from the seat belt of the seat-belt assembly. This spatial arrangement results in a substantial drawback with respect to motor-vehicles, since an installation that uses various locations of the motor-vehicle is required for this measuring system. Besides the domain that encompasses the motor-vehicle seat and the seat-belt assembly associated therewith, the location for the instrument panel and/or the headliner must be incorporated into the intended installation of the measuring and sensor system, for example. Moreover, the subsequent installation of the measuring and sensor system with relatively low technical and constructive effort is not possible.
A measuring and sensor system is known from U.S. Pat. No. 7,576,642 that is mounted on a seat belt of a seat-belt assembly. In this measuring system, electrical conductors for contacting the sensors of the measuring and sensor system are woven into the seat belt of the seat-belt assembly.